Catalyst for purifying gases from hydrogen sulphide

ABSTRACT

A process for purifying gases from hydrogen sulphide which comprises oxidation of hydrogen sulphide with air oxygen at a volume ratio between hydrogen sulphide to oxygen equal to 1:1-1.5 on a catalyst having the following composition, % by weight: titanium dioxide--10-30, iron oxide--20-30, zinc oxide--20-25, chromium oxide--20-50. The process is conducted at a temperature within the range of from 220° to 260° C. and at a space velocity of the gas mixture of from 3,000 to 15,000 hr -1 .

This is a division of application Ser. No. 613,892, filed May 24, 1984,now U.S. Pat. No. 4,519,992.

FIELD OF THE INVENTION

The present invention relates to the art of purification of gases fromsulphurous compounds and, more specifically, it relates to a process forpurification of gases from hydrogen sulphide and is useful in the gasand petroleum-refining industries.

BACKGROUND OF THE INVENTION

Natural gas or gases resulting from petroleum refining prior to theirprocessing are subjected to a preliminary purification from sulphurouscompounds, in particular, hydrogen sulphide.

One of the prior art processes for purification of gases from hydrogensulphide comprises its chemical interaction with solid reactants (cf. B.S. Al'tschuler, A. A. Gavrilova "High-Temperature Purification of Gasesfrom Sulphurous Compounds", 1969, "Nauka" Publishers, Moscow, p.51-101). This process enables fine purification of the gas,substantially 100% recovery of hydrogen sulphide, but its implementationnecessitates application of high temperatures and is accompanied by theformation of large quantities of SO₂ as a result of interaction ofoxygen with sulphides upon regeneration of the absorbents.

Known in the art is a process for purification of a gas from hydrogensulphide by way of oxidation thereof on a catalyst - activated carbon(cf. Journal of Catalysis, v. 35, No. 1, 1974; M. Stejns, P. Mars "TheRole of Sulfur Trapped in Micropores in the Catalytic Partial Oxidationof Hydrogen Sulfide with Oxygen, p. 11-17).

The process is effectively performed within a broad temperature range offrom 20° to 250° C. However, at temperatures of up to 200° C. theresulting sulphur is cooled on the catalyst, deactivates it so that theefficiency of purification is considerably lowered. At a temperatureabove 200° C. sulphur is oxidized into SO₂, wherefore the processselectivity is impaired.

It is known to purify gas from hydrogen sulphide with the use of zeolitecatalysts (Proceedings of Moscow Mendeleev Technological ChemicalInstitute, issue 56, 1967; M. A. Adlivankina, N. V. Kel'tsev, N. S.Torocheshnikov, Yu. I. Schumyatsky "A Study on the Process of PartialOxidation of Hydrogen Sulphide on Zeolities", pp. 160-164). The processis conducted at low space velocities (890 hr⁻¹) and elevatedtemperatures (324° C.). But even under these conditions no completerecovery of hydrogen sulphide from gases is achieved.

Known is a process for purification of gases from hydrogen sulphide on acatalyst comprising bauxite (Gazovaya Promyshlennost' /Gas Industry/,No. 8, August 1966; Yu. N. Brodsky, V. I. Gerus, S. M. Goland, Ya. I.Frenkel "Production of Sulphur at the Pokhvistnevskaya Gas CompressorStation", pp. 42-44). The maximum degree of gas purification in carryingout the process as taught by this reference does not exceed 93% even atthe low space velocity of 300 hr⁻¹ and at the temperature of 280° C. Toachieve a 96% degree of conversion of hydrogen sulphide, it is necessaryto carry out the process in two stages with separation of water at theintermediate stage to prevent deactivation of bauxite, since an increasein the concentration of water vapours from 0.9 to 12.9% lowers thedegree of the gas purification after the first step from 85% to 42% (cf.U.S. Pat. No. 3,781,445 issued Dec. 25, 1973).

The gas purification from hydrogen sulphide by this process with the useof alumina does not provide for a high selectivity of the process. Thus,at the temperature of 235° C. and space velocity of 3,000 hr⁻¹ nearly20% of hydrogen sulphide are converted into sulphurous anhydride(Newsletters of Higher School, "petroleum and Gas", No. 2, February1979; T. G. Alkhazov, A. A. Vartanov "On Catalytic Oxidation of NaturalGas Hydrogen Sulphide", p. 41-44).

Carrying out the process with the use of iron-oxide catalyst does notprovide high process characteristics within a wide range of space ratesand temperatures either. At the space velocity of 15,000 hr⁻¹ and at thetemperature of 300° C. the degree of the gas purification is not morethan 95%. Decreasing the space velocity contributes to a lesserselectivity of the process (cf. USSR Inventor's Certificate No. 865777,Cl. C01 B 17/04, 1981).

Also known in the art is a process for oxidation of hydrogen sulphide toelemental sulphur on a catalyst containing oxides of titanium and ironwith the following content of the components, % by weight: iron oxide0.05-0.3, titanium dioxide--the balance (cf. USSR Inventor's CertificateNo. 856974, Cl. C 01 B 17/04, 1981). The maximum conversion of hydrogensulphide into sulphur equal to 99.5% with the 100% selectivity isattained at space velocities of 2,500 to 3,000 hr⁻¹ and temperatureswithin the range of from 285° to 300° C. This process makes it possibleto purify gases with a high content of hydrogen sulphide of up to 25% byvolume. A high conversion and selectivity can be attained only incarrying out the process in two stages with an obligatory intermediatetrapping of sulphur and water and with separate supply of oxygen to eachstage. A strictly predetermined ratio of O₂ to H₂ S should be maintainedat each stage, this involving certain difficulties in the processcontrol. Furthermore, as it has been already mentioned hereinbefore, a100% conversion of hydrogen sulphide and a 99.5% selectivity of itsoxidation into elemental sulphur are ensured at low space velocities ofup to 3,000 hr⁻¹ and at elevated temperatures of up to 300° C.

OBJECT OF THE INVENTION

It is an object of the present invention to provide such a process forpurification of gases from hydrogen sulphide which would make itpossible to simplify the process control and improve its efficiency.

SUMMARY OF THE INVENTION

This object is accomplished by the provision of a process forpurification of gases from hydrogen sulphide by way of oxidation thereofwith oxygen at a volume ratio of hydrogen sulphide to oxygen equal to1:1-1.5 on a catalyst containing the following components, percent byweight: titanium dioxide--10-30, iron oxide--20-30, zinc oxide --20-25,chromium oxide--20-50, at a temperature of 220° to 260° C. and at aspace velocity of passing the gas mixture of from 3,000 to 15,000 hr⁻¹.

The process according to the present invention makes it possible toachieve a high degree of purification from hydrogen sulphide of not lessthan 98% with a selectivity of not less than 98%. The process is highlyefficient, since it is performed in a single stage and proceeds at highspace velocities of up to 15,000 hr⁻¹.

An important advantage of the process according to the present inventionis irreversibility of the process ensuring a quantitative conversion ofhydrogen sulphide into elemental sulphur without the formation of aby-product, i.e. sulphurous anhydride.

DETAILED DESCRIPTION OF THE INVENTION

The starting gas, e.g. natural gas or gas resulting from petroleumrefining is mixed with air so that the volume ratio of oxygen tohydrogen sulphide in the gas mixture be equal to 1-1.5:1. The resultinggas mixture is passed onto a catalyst containing the followingcomponents, percent by weight: titanium dioxide--10-30, ironoxide--20-30, zinc oxide--20-25, chromium oxide--20-50. The oxidationprocess is conducted in one stage at a temperature within the range offrom 220° to 260° C. and at a space velocity of the gas mixture of 3,000to 15,000 hr⁻¹. Under the above-specified conditions hydrogen sulphideis oxidized and quantitatively converted into sulphur.

The process according to the present invention makes it possible toobtain in a single stage practically a 100% conversion of hydrogensulphide into sulphur without the formation of sulphurous anhydride.

For a better understanding of the present invention some specificexamples are given hereinbelow by way of illustration.

EXAMPLE 1

Subjected to purification is a hydrocarbon gas containing 3 vol. % ofhydrogen sulphide. This gas is mixed with air so that the volume ratioof hydrogen sulphide to oxygen be equal to 1:1.5 and then fed onto acatalyst having the following composition, % by weight: Fe₂ O₃ --25,TiO₂ --25, ZnO--25, Cr₂ O₃ --25. The process is conducted at thetemperature of 240° C. and at the space velocity of 3,000 hr⁻¹. As aresult, the degree of purification of the gas from hydrogen sulphide isequal to 100%, the process selectivity is 98.8%.

To prepare the catalyst, in separate vessels there are dissolved: 25.5 gof iron chloride in 943 ml of distilled water, 26.3 g of chromiumchloride in 1,000 ml of water, 12.5 of zinc chloride in 916 ml of waterand 17.8 g of titanium chloride in 940 ml of water. To the thus-preparedsolutions a 3N aqueous solution of ammonia is added to ensure completeprecipitation of hydroxides of iron, chromium, zinc and titanium. Thehydroxides are poured into one vessel, thoroughly intermixed and themixture is washed with distilled water till a negative reaction forchloride ions is observed. Then the catalyst is filtered off, moulded,air-dried at room temperature and calcined at the temperature of 500° C.for 4 hours. As a result, a catalyst of the above-specified compositionis obtained. The catalysts in the subsequent Examples are preparedfollowing a similar procedure.

EXAMPLE 2

A hydrocarbon gas containing 3% by volume of hydrogen sulphide issubjected to purification. This gas is mixed with air so that the volumeratio of hydrogen sulphide to oxygen is equal to 1:1.5 and fed onto acatalyst having composition specified in Example 1 hereinabove. Theprocess is conducted at the temperature of 220° C. and the spacevelocity of 9,000 hr⁻¹. As a result, the degree of purification of thegas from hydrogen sulphide is 99.6%, the process selectivity is 100%.

EXAMPLE 3

A hydrocarbon gas containing 3% by volume of hydrogen sulphide issubjected to purification. This gas is mixed with air so that the volumeratio of hydrogen sulphide to oxygen is equal to 1:1 and then fed onto acatalyst with the composition specified in Example 1. The process isconducted at the temperature of 260° C. and the space velocity of 15,000hr⁻¹. As a result, the degree of purification of the gas from hydrogensulphide is 99.9%, the process selectivity is 100%.

EXAMPLE 4

A hydrocarbon gas containing 3% by volume of hydrogen sulphide issubjected to purification. This gas is mixed with air so that the volumeratio of hydrogen sulphide to oxygen is equal to 1:1.5 and fed onto acatalyst having the following composition, % by weight: Fe₂ O₃ --20, Cr₂O₃ --50, TiO₂ --10, ZnO--20. The process is conducted at the temperatureof 240° C. and the space velocity of 15,000 hr⁻¹. As a result, thedegree of the gas purification from hydrogen sulphide is 98.6%, theprocess selectivity is 100%.

EXAMPLE 5

A gas containing 3 vol. % of hydrogen sulphide is subjected topurification. This gas is mixed with air so that the volume ratio ofhydrogen sulphide to oxygen be equal to 1:1 and fed onto a catalysthaving the following composition, % by weight: Fe₂ O₃ --30, Cr₂ O₃ --20,TiO₂ --30, ZnO--20. The process is conducted at the temperature of 240°C. and the space velocity of 15,000 hr⁻¹. As a result, the degree of thegas purification from hydrogen sulphide is 99.1% the process selectivityis 100%.

Examples 6, 7 and 8 are presented in a tabulated form. A gas containing3% by volume of hydrogen sulphide is subjected to purification. This gasis mixed with air so that the volume ratio of hydrogen sulphide tooxygen is equal to 1:1 and fed onto a catalyst having the compositionspecified in the Table hereinbelow. The process is conducted at atemperature within the range of from 220° to 260° C. and the spacevelocity of 6,000 hr⁻¹. The process parameters are shown in thefollowing Table.

                                      TABLE                                       __________________________________________________________________________                          Degree of gas purification from H.sub.2 S                                     (α)                                                                     and selectivity of the process, (S) %, at                                     temperatures, °C.                                Catalyst composition, % by weight                                                                   220    240    260                                       Fe.sub.2 O.sub.3                                                                       Cr.sub.2 O.sub.3                                                                   TiO.sub.2                                                                         ZnO α                                                                           S  α                                                                           S  α                                                                           S                                     Example No.                                                                   1    2   3    4   5   6   7  8   9  10  11                                    __________________________________________________________________________    6    20  50   10  20  98.5                                                                              100                                                                              99.6                                                                              100                                                                              99.8                                                                              98.6                                  7    25  25   25  25  100 100                                                                              100 100                                                                              100 99.9                                  8    30  20   30  20  100 100                                                                              100 100                                                                              100 97.8                                  __________________________________________________________________________

What is claimed is:
 1. A catalyst useful in the oxidation of hydrogensulphide contained in gases, said catalyst comprised of the followingcomponents in percent by weight:

    ______________________________________                                        titanium dioxide                                                                              10-30                                                         iron oxide      20-30                                                         zinc oxide      20-25                                                         chromium oxide  20-50                                                         ______________________________________                                    


2. The catalyst of claim 1 wherein said components are present inpercent by weight as follows:

    ______________________________________                                               titanium dioxide                                                                        10                                                                  iron oxide                                                                              20                                                                  zinc oxide                                                                              20                                                                  chromium oxide                                                                          50                                                           ______________________________________                                    


3. The catalyst of claim 1 wherein said components are present inpercent by weight as follows:

    ______________________________________                                               titanium dioxide                                                                        25                                                                  iron oxide                                                                              25                                                                  zinc oxide                                                                              25                                                                  chromium oxide                                                                          25                                                           ______________________________________                                    


4. The catalyst of claim 1 wherein said components are present inpercent by weight as follows:

    ______________________________________                                               titanium dioxide                                                                        30                                                                  iron oxide                                                                              30                                                                  zinc oxide                                                                              20                                                                  chromium oxide                                                                          20                                                           ______________________________________                                    


5. A process for the preparation of the catalyst of claim 1, whichcomprises the steps of:(a) forming separate aqueous solutions of ironchloride, chromium chloride, zinc chloride and titanium chloride; (b)adding ammonia to each of said solutions to precipitate the respectivemetal hydroxides; (c) combining said hydroxides and washing with wateruntil all chloride ions are removed; and (d) drying and calcining saidhydroxides to the corresponding oxides.